The present invention relates generally to pipe joints, and more particularly to a novel remote control pipe joint.
Piping systems are generally employed in fusion reactors for transportation of radioactive materials under a wide range of temperatures and pressures. It is desirable that pipe joints in such systems be capable of assembly and disassembly by remote control in order to avoid exposure of workers to radiation hazards. Leakage has been a problem in known remote control pipe joints, particularly where large pressure and temperature differences are to be maintained between the interior and the exterior of the joint. Conventional pipe joints which have been satisfactory from the standpoint of leakage are difficult to assemble by remote control. Thus, there is a need for an improved remote control pipe joint.
One common type of pipe joint seal is formed by positioning an O-ring between flanges on adjacent ends of the pipes to be joined, and bolting the flanges together. The pressure exerted on the O-ring by the flanges conforms the O-ring to asperities in the flange surfaces and thereby forms the seal. Elastomeric O-rings are used in some applications, but are subject to destruction by exposure to nuclear radiation or high temperature. Metal O-rings are generally preferred for pipe joints in the presence of high temperatures and/or radioactivity. The quality of the seal is somewhat dependent upon the ability of the metal to conform to the asperities of the flange surfaces and to behave elastically within a certain range to compensate for small displacements of the flanges relative to one another. Relatively soft metals such as copper are generally preferred.
One of the major shortcomings of seals made with metal O-rings is that the pressure required to form the seal typically causes excessive plastic deformation of the metal O-ring and results in strain hardening of the metal. The deformation is greatest near bolts because the closing force is greatest at these areas. The plastic deformation has two undesirable effects. First, if the seal is opened and subsequently reclosed, the O-ring frequently will not form a satisfactory seal upon reclosure because the hardness of the metal prevents it from conforming to surface asperities. Secondly, the O-ring no longer responds elastically to small displacements of the pipes relative to one another, and thus slight disturbances of the piping system may open small gaps between the O-ring and the flange surfaces against which it acts so as to permit leakage.
A problem which is particularly related to copper O-rings derives from the fact that copper has a relatively high coefficient of thermal expansion. When large fluctuations in temperature occur, the resulting thermal strain may cause friction between the sealing ring and the adjacent flange surfaces which may be deleterious to the seal and result in leakage.